elo: Elo Ratings

A flexible framework for calculating Elo ratings and resulting
rankings of any two-team-per-matchup system (chess, sports leagues, 'Go',
etc.). This implementation is capable of evaluating a variety of matchups,
Elo rating updates, and win probabilities, all based on the basic Elo
rating system. It also includes methods to benchmark performance,
including logistic regression and Markov chain models.